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SUMMARY In simulations of propagating blast waves the effects of artificial reflections at open boundaries can seriously degrade the accuracy of the computations. In this paper, a boundary condition based on a local approximation by a plane traveling wave is presented. The method yields small artificial reflections at open boundaries. The derivation and the theory behind these so-called plane-wave boundary conditions are presented. The method is conceptually simple and is easy to implement in two and three dimensions. These non-reflecting boundary conditions are employed in the three-dimensional computational fluid dynamics (CFD) solver FLACS, capable of simulating gas explosions and blast-wave propagation in complex geometries. Several examples involving propagating waves in one and two dimensions, shock tube and an example of a simulation of a propagating blast wave generated by an explosion in a compressor module are shown. The numerical simulations show that artificial reflections due to the boundary conditions employed are negligible. © 1998 John Wiley & Sons, Ltd.

On November 7, 1975 a violent vapor cloud explosion occurred within a naphta cracker installation located at Beek in The Netherlands. The explosion resulted in several fatalities, destroyed the installation, resulted in severe damage in the direct surroundings of the installation and window breakage up to 4.5 km from the installation. The explosion was investigated, in detail, concentrating on the cause of the release of flammable gas and the explosion effects. The results were published in an official report by the Dutch authorities (Ministry of Social Affairs). In addition, a summary of accident descriptions were published by Lees and Gugan. Early in the 1980`s Christian Michelsen Research started developing a numerical tool which allows one to predict the effects of gas explosions in complex geometries. The first version of this tool (FLACS=FLame ACceleration Simulator) was issued in 1986. A second version was issued in 1989 and recently a third version was issued. The tool has been validated against numerous experiments on small- and medium-scale (maximum volume 50 m{sup 3}). The main application of the tool is prediction of explosion effects in offshore geometries but the tool has also been used for prediction of effects of explosions in landbased installations. Themore » tool appears to reproduce scaling effects (from small- to medium-scale) very well. The major uncertainty is, however, whether this range of scales is representative for industrial plants. No full-scale experimental data exist, hence scaling is a matter of some concern when FLACS results are used. Full-scale experiments are very expensive to perform and to shed some light on this question it was decided to simulate a well-documented accident. To this end the vapor cloud explosion accident which happened at Beek was chosen. Simulation of such an accident would at least show the possibilities of the use of FLACS for such large landbased installations. 14 refs., 9 figs., 3 tabs.« less

The analytical solution of many problems of acoustics is expressed in terms of a Fourier integral. In this paper, general asymptotic expressions that appxoximate both the location and the value of the maximum amplitude of a one‐ or two‐dimensional Fourier integral are presented. These expressions are generally easier to compute than evaluations using a fast Fourier transform algorithm. The method is used to study the reflection and transmission of a real sound beam at the interface between two homogeneous and dissipative fluid layers. Simplified analytical formulas that explain the beam displacement and other behavior near the interface are obtained. Numerical results are compared with those of an earlier work [see Sagen, Naze Tjotta, and Tjotta, J. Acoust. Soc. Am. 85, 24–38 (1989)]. The influence of various parameters on the direction and shape of the reflected and transmitted sound beams is investigated. [Work supported by the IR&D program of ARL:UT, The Royal Norwegian Council for Scientific and Industrial Research (NTNF), and VISTA/STATOIL, Norway.]